your hps will be by far the most sufficient source of light, you can combat the heat with your hood.. The typical thing to do with cooltubers I have seen, is to connect them to an extractor fan that force the hot air trapped around the lamp (due to the heat resistant glass) to leave the grow space completely. If the other end of the cool-tuber (some just have small holes to draw air from the inside of the growing area) is either connected to an intake fan that brings air from outside your box OR to a carbon filter(optional, could easily leave it w/o unless you want to combat smell that way) that is left to extract air from the grow area.
So to keep it simple:
-you MUST draw air OUTSIDE from using an extractor fan that is somehow attached to your cooltuber.
- Depending on its structure you can decide whether you want to draw air from INSIDE the area or OUTSIDE.
a)People that draw from outside the area IMO have big heat issues (i only see this happen in grow logs that have 1kW Hps's in grow rooms and intake cold air from outside the house),
b) I would just use your hood to extract air from INSIDE the box, so you don't have to open an extra hole in the back. If you do decide to intake air from outside, you will have to make sure you have a mini vent system for the rest of the area as fresh air circulation is 'a must' for any grow environment even w/o heat issues..
